docs: def _get_uncertainties(self, star_group_size):
          """
          Retrieve uncertainties on fitted parameters from the fitter
          object.
  
          Parameters
          ----------
          star_group_size : int
              Number of stars in the given group.
  
          Returns
          -------
          unc_tab : `~astropy.table.Table`
              Table which contains uncertainties on the fitted parameters.
              The uncertainties are reported as one standard deviation.
          """
  
          unc_tab = Table()
          for param_name in self.psf_model.param_names:
              if not self.psf_model.fixed[param_name]:
                  unc_tab.add_column(Column(name=param_name + "_unc",
                                            data=np.empty(star_group_size)))
  
          if 'param_cov' in self.fitter.fit_info.keys():
              if self.fitter.fit_info['param_cov'] is not None:
                  k = 0
                  n_fit_params = len(unc_tab.colnames)
                  for i in range(star_group_size):
                      unc_tab[i] = np.sqrt(np.diag(
                                            self.fitter.fit_info['param_cov'])
                                           )[k: k + n_fit_params]
                      k = k + n_fit_params
          return unc_tab